Laser oscillators utilizing an optical fiber have been widely used. This type of laser oscillator is configured to oscillate a laser light by the optical fiber with use of an excitation light to be oscillated from a light source. The optical fiber to be used for this type of laser oscillator is made of, for instance, fluoride glass such as ZBLAN glass doped with a laser medium such as erbium. However, there is a drawback that fluoride glass as described above, particularly ZBLAN glass, deliquesces by moisture contained in the atmosphere by which the laser light from the optical fiber is absorbed. Put differently, there is a drawback that an end surface of the optical fiber is damaged.
For instance, an end cap is joined to the end surface of the optical fiber in order to solve the drawback. With the construction, the end surface of the optical fiber is not exposed to the atmosphere. Hence, the end surface of the optical fiber can be prevented from deliquescing by the moisture contained in the atmosphere.
The laser medium contained in the optical fiber generates heat by absorbing the excitation light. Hence, it is required to prevent that the optical fiber is burnt and damaged by the heat generation. For instance, the optical fiber is interposed and held between two metallic plates and heat from the optical fiber is transferred thereto. Thus, damage of the optical fiber attributed to heat generation is prevented.